1. Field of the Invention
The present invention relates to a method and an apparatus for magnet-optical recording. More specifically, the present invention relates to a method and an apparatus for magnet-optical recording, in which magnetized marks are recorded on a magnet-optical recording medium by using a pulsed magnetic field and by irradiating a pulsed light beam.
2. Description of the Prior Art
A magnet-optical recording apparatus (a magnet-optical disk drive), especially a magnetic field modulation type magnet-optical recording apparatus has a high recording density and enables high speed data transmission, so it is expected to be a main stream of recording media in a computerized society. However, it is important to improve the magnetic inversion speed of a magnetic head in order to take advantage of the high transmission speed.
In general, an optical head for irradiating a laser beam to a magnet-optical recording medium and a magnetic head for applying a magnetic field are disposed at the opposite sides with respect to the magnet-optical recording medium. Therefore, it is difficult to position the laser beam spot and the magnetic head precisely because of a registration error and an eccentricity. Accordingly, the magnetic head is usually made larger (e.g., approximately 200 xcexcmxc3x97200 xcexcm) so that the effective area of the magnetic field applied by the magnetic head can cover the movable area of the laser beam spot.
As a result, an inductance of the magnetic head increases, and the magnetic inversion speed becomes slow. In order to avoid an imprecise edge of the magnetized mark due to the slow magnetic inversion speed, a method is invented in which a pulsed laser beam is used for writing a magnetized mark when the magnetic field is large (see Japanese patent publication No. 7-21892, for example).
In addition, a front illumination method as shown in FIG. 1 is invented for further improving the data transmission. In this method, a small magnetic head is arranged at the laser beam irradiation side of the magnet-optical recording medium. Namely, as shown in FIG. 1, the magnet-optical recording medium 11 is irradiated by the laser beam 12 not at the transparent substrate 11a side but at the recording layer 11b side above which the magnetic head 13 is disposed. The magnetic head 13 includes a magnetic head coil 14 made of a thin film pattern. The laser beam 12 that was concentrated by a focus lens 15 passes through an opening formed in the middle portion of the magnetic head coil 14 and is irradiated onto the recording layer 11b of the magnet-optical recording medium 11.
The above-mentioned front illumination method enables the optical head including the focus lens 15 and the magnetic head 13 to be mounted on a common slider, so that the irradiation spot of the laser beam 12 and the position of the magnetic head 13 can be aligned precisely. Therefore, the effective area of the magnetic field applied by the magnetic head 13 can be small (less than 50 xcexcmxc3x9750 xcexcm, for example), so that an inductance of the magnetic head coil 14 can be decreased. As a result, the magnetic inversion speed can be improved.
However, since the magnetic head coil 14 is formed by a thin film technology so as to make the magnetic head 13 light and low profile, a resistance of the magnetic head coil 14 increases. A large resistance generates heat that may cause the detrimental effects such as fusing of the magnetic head coil 14, deformation of the focus lens 15 and an excessive heat of the magnet-optical recording medium 11.
In order to avoid the above-mentioned detrimental effects, a method is proposed in which a pulsed magnetic field is generated for applying the magnetic field to the magnet-optical recording medium as disclosed in Japanese Patent No. 2803841, for example. This method can suppress the heat of the magnetic head coil 14 by exciting the magnetic head coil 14 not continuously but intermittently for necessity.
However, the control of the heat of the magnetic head coil is not sufficient by the above-mentioned method. More effective method for decreasing the heat has been desired. In the conventional method, the magnetic field is required to be applied continuously from the irradiation of the pulsed light until the temperature of the recording layer of the magnet-optical recording medium becomes below the Curie point (Tc). Therefore, the heat reducing effect by the pulse driving of the magnetic head coil has a limitation.
The object of the present invention is to provide a method and an apparatus for magnet-optical recording that utilize a novel concept for reducing a heat in the pulse driving of the magnetic head coil.
According to a first aspect of the present invention, a magnet-optical recording method is provided, in which magnetized marks are recorded on a magnet-optical recording medium by irradiating a pulsed light beam onto the recording medium and by applying a pulsed magnetic field to the recording medium. This method utilizes a reverse magnetic field generated by the magnetized mark that was recorded just before the present mark so as to reduce the exciting energy of the magnetic field to be applied when the present mark is recorded in the polarity that is opposite to the polarity of the magnetized mark that was recorded just before the present mark.
When the magnetic recording film is heated above the Curie point (Tc), the heated spot can be magnetized in the polarity opposite to that of the present magnetized mark due to the influence of the magnetic field generated by the surrounding magnetized marks without application of the external magnetic field. This phenomenon is known as a reverse magnetic field phenomenon and is utilized in a so-called overwrite type magnet-optical recording medium as disclosed in Japanese patent publication No. 6-79391, Japanese unexamined patent publication No. 3-127347 or Japanese Patent No. 2630976, for example.
The above-mentioned first magnet-optical recording method of the present invention utilizes the reverse magnetic field explained above so as to reduce the exciting energy of the applied magnetic field when recording a magnetized mark having a polarity opposite to that of the magnetized mark that was recorded just before the present mark. Thus, the total heat of the magnetic head coil can be reduced.
In an embodiment of the method for reducing the exciting energy of the applied magnetic field, an exciting current that is supplied to a magnetic head coil for generating the magnetic field is reduced. In another embodiment, an exciting period of a magnetic head coil for generating the magnetic field is reduced. It is also possible that an exciting current is not supplied to a magnetic head coil for generating the magnetic field when the present mark is recorded in the polarity that is opposite to the polarity of the magnetized mark that was recorded just before the present mark.
According to a second aspect of the present invention, the magnet-optical recording method uses a magnet-optical recording medium having a recording layer and an auxiliary recording layer, and magnetized marks are recorded on the magnet-optical recording medium by applying a pulsed magnetic field to the recording medium and by irradiating a pulsed light beam onto the recording medium. The method includes the steps of recording a magnetized mark on the auxiliary recording layer by applying the magnetic field in a short pulse form in accordance with data to be recorded, and transferring the magnetized mark recorded on the auxiliary recording layer to the recording layer by irradiating a pulsed light beam.
The magnet-optical recording medium that has a recording layer and an auxiliary recording layer has been used as an optical modulation overwrite type magnet-optical recording medium as disclosed in Japanese unexamined patent publication No. 6-44630 or No. 6-203418, for example. In this magnet-optical recording medium, a magnetic field that is weak at the normal temperature is used for writing a magnetized mark on the auxiliary recording layer. After that, a laser beam is irradiated for heating the recording layer above the Curie point (Tc), so that the magnetized mark of the auxiliary recording layer can be transferred to the recording layer.
The above-mentioned magnet-optical recording method of the present invention utilizes the auxiliary recording layer for reducing the exciting power of the magnetic head coil that generates the magnetic field applied for recording magnetized marks. Namely, when recording a magnetized mark on the auxiliary recording layer, it is not needed to keep the applied magnetic field until the temperature drops below the Curie point (Tc). Therefore, the magnetic head coil can be driven by pulse and the exciting period can be shortened substantially. In general, it is said that several nanoseconds are necessary for writing a magnetized mark on the auxiliary recording layer, i.e., for magnetizing a magnetic material. Therefore, a magnetized mark is written on the auxiliary recording layer in accordance with write data by using the pulsed magnetic field, and then the magnetized mark of the auxiliary recording layer is transferred to the recording layer by irradiating the pulsed light, so that the exciting power of the magnetic head coil and the heat thereof can be reduced.
Preferably, the pulsed magnetic field is generated when a magnetic inversion of the write data occurs and just before the irradiation spot of the pulsed light deviates from the magnetized area of the auxiliary recording layer that was magnetized by the pulsed magnetic field.
The auxiliary recording layer is magnetized over the effective area of the applied magnetic field that is approximately several dozens microns including the irradiation spot. Therefore, if there is no magnetic inversion, the next generation of the magnetic field can be delayed until the record mark (i.e., the irradiation spot of the pulsed light) deviates from the magnetized area of the auxiliary recording layer, so that the heat of the magnetic head coil can be further reduced.
A first magnet-optical recording apparatus according to the present invention enables the above-mentioned first magnet-optical recording method. The apparatus includes means for detecting a magnetic inversion of data to be recorded and means for reducing an exciting energy of a magnetic head coil that generates the magnetic field in accordance with an output signal of the means for detecting a magnetic inversion of data.
In an embodiment, the exciting circuit of the magnetic head coil has a plurality of current paths that are connected in parallel, and the means for reducing an exciting energy cut off a part or all of the current paths so that the exciting energy of the magnetic head coil is reduced.
In another embodiment, an exciting circuit for the magnetic head coil includes a switching device that is driven by a pulse so as to generate the pulsed magnetic field, and the means for reducing an exciting energy shorten the turned-on period of the switching device so that the exciting energy of the magnetic head coil is reduced.
A second magnet-optical recording apparatus according to the present invention enables the above-mentioned second magnet-optical recording method. The apparatus includes means for detecting a magnetic inversion of data to be recorded, an exciting circuit for a magnetic head coil, the circuit including a switching device that is driven by a pulse so as to generate the pulsed magnetic field, and a pulse generation circuit for generating a pulse that turns on the switching device for a short period when the magnetic inversion of data occurs, in accordance with an output signal of the means for detecting a magnetic inversion of data.
In a preferable embodiment, the pulse generation circuit includes a timer that starts when the magnetic inversion of data occurs, and a pulse is generated for turning on the switching device for a short period after a lapse of a predetermined period from the magnetic inversion of data, regardless of the presence or absence of another magnetic inversion of data. By this configuration, the variation of the second magnet-optical recording method can be realized mimetically by the timer, in which the next generation of the magnetic field is delayed until the record mark deviates from the magnetized area of the auxiliary recording layer.